“On the other hand, verapamil (1 mg/l) and D 600 (0.4 mg/l) completely blocked the excitation process within 20–25 min.”
“The fact, that the inhibitory effect of verapamil and D 600 cannot be neutralized by catecholamines or excess Ca seems to indicate that some properties of the slow membrane channel are not exactly identical in sinoatrial pacemaker cells and in the ventricular myocardium.”